1. Field of the Invention
This invention relates to an apparatus and a method for measuring a density of defects existing in a semiconductor wafer and an apparatus and a method for measuring an inherent scattering intensity of defects existing in a semiconductor wafer, especially relates to an apparatus and a method which are effective to accurately evaluate crystal defects existing in a semiconductor wafer.
2. Description of the Prior Art
It is known the technique in which crystal defects (hereinafter referred to as "defects") existing in a semiconductor wafer is measured by using a laser. In this technique, the defects existing in the semiconductor wafer is measured by performing a series of the following steps.
(1) Irradiating a laser on the surface of a semiconductor wafer, and receiving a scattered light which is scattered by the defects existing in the semiconductor wafer. PA1 (2) Transferring the scattered light received in step1 to the frequency of the defects. PA1 (3) Deciding a detecting possibility depth of the defects by utilizing a attenuation characteristics of the laser. PA1 (4) Calculating a detecting possibility volume of the defects by using the detecting possibility depth deciding in step 3 and the area of irradiating the laser. PA1 (5) Deriving a density of the defects by using the detecting possibility volume calculated in step 4 and the frequency of the defects deriving in step 2.
However, There is a case that the density of the defects obtained by performing the above steps can deviate from the actual density of the defects because the detecting possibility depth is decided as a fixed value. This depends on distributing the defects having various inherent scattering intensitys in the semiconductor wafer. For example, a large defect has an inherent scattering intensity which is larger than that of a small defect, and can be detected in a deeper depth.
Therefore, when a large defect exists in a depth which is deeper than the detecting possibility depth decided previously, the signal obtained from the defect is included in the information of the density. And then the density of the defects which is finally obtained becomes larger than the actual density.
On the other hand, if the detecting possibility depth is greatly set in consideration of the existence of an extra signal like the above-mentioned, the density of the defects which is finally obtained becomes smaller than the actual density because a small defect cannot be detected even if existing in the set depth.
Thus, it is difficult to decide the detecting possibility depth in the above conventional technology, and it is necessary to improve the conventional technology in order to accurately evaluate the defects.